1. Field of Invention
The invention relates to a projection-type display apparatus which modulates light emitted from a light source in accordance with image signals using modulation devices such as liquid crystal light valves or the like, and performs enlarged projection of the light flux following modulation upon a screen via a projecting lens. More particularly, the invention relates to a structure for a projection-type display apparatus of such a type whereby the image formation range of the modulating devices can be illuminated in an appropriate manner.
2. Description of Related Art
A conventional projection-type display apparatus which forms modulated light flux in accordance with image signals using liquid crystal light valves and performs enlarged projection of the modulated light flux on a screen is disclosed in Japanese Unexamined Patent Publication No. 3-111806. The projection-type display apparatus disclosed in this Patent Publication is, as shown in FIG. 14, provided with an integrator optical system 923. The integrator optical system 923 has two lens plates 921 and 922 for uniform illumination of the image formation range of the liquid crystal light valve 925. The liquid crystal light valve 951 serves as the modulation device of the light emitted from the light source.
In FIG. 14, the single light flux emitted from the light source lamp unit 8 is separated into a plurality of intermediate light fluxes by lenses 921a of the first lens plate 921. The light flux is superimposed on the liquid crystal light valve 951 via lenses 922a of the second lens plate 922.
Regarding projection-type display apparatuses of the type illustrated in FIG. 14, problems occur when the image formation range of the liquid crystal light valve 951 cannot be illuminated accurately. These problems include a reduction in the brightness of the image projected on the projection surface, or the creation of shadows at the edge of the projected image. Accordingly, as illustrated in FIG. 15, a certain margin M is secured around the image formation area A of the liquid crystal light valve 925, depending on various factors including the positioning precision of the liquid crystal light valve 951 and the lens plates 921 and 922 of the integrator optical system 923, the margin of error of the focal distance and so forth of the lenses 921a and 922a of each of the lens plates, and the positioning precision and the like of other optical components disposed on the optical path. In other words, the image formation area A of the liquid crystal light valve 951 is sized to be distinctly smaller than the illumination range B of light emitted by the light source, so that even in the event that the illumination range B is shifted vertically or horizontally due to the positioning precision of the above-described components, the image formation range A does not extend beyond the illumination range B. This structure avoids problems such as the reduction of the brightness of the image projected on the projection surface, or the creation of shadows at the edge of the projected image. Thus, simply increasing the margin M is sufficient to deal with a wide margin of error in positioning of the above-described components.
On the other hand, in order to increase the brightness of the projected image, it is necessary to increase the usage efficiency of the light which is illuminating the liquid crystal light valve 925. However, the problem occurs that when the margin M is increased to deal with a wide margin of error in positioning of the above-described components, the usage efficiency of the separated light decreases, and the projected image becomes dark. Accordingly, from this perspective, it is desirable that the margin formed around the display range of the liquid crystal light valve be as narrow as possible. However, if the margin is made to be narrow, the illumination range misses the image formation range of the liquid crystal light valve, as described above, so that shadows may be formed at the edge of the projected image.